Investigators have used fingerprints to identify criminals for over a century. While other visible characteristics may change over time, fingerprints do not. Fingerprints are the residue of perspiration secreted along the tops of “friction ridges” on fingertips. When people touch something, they leave what is called a “latent” print. Latent prints are not usually visible to the naked eye.

Analysts reveal latent prints by using powders, special lighting, or chemicals, depending on the surface on which the print was left. They look at specific areas of prints for points that match between a suspect’s fingerprint and the latent print from the crime scene. There is no international standard for the number of points that result in an identification match. Postal Inspection Service technicians look for seven to nine points before declaring a match.

Can You Match the Print to the Right Suspect?

A fugitive has left his thumbprint on this map which was found at the scene of a crime. This is an important clue! Postal inspectors have three suspects and need to use the print to determine which of these individuals should be charged with the crime.

Image (left): Illustration of nine matching points between known and latent prints

Can you help the inspectors find the thieves?

Use the known thumbprints on the posters below to match the latent print found in the bottom right corner of the map above.